Word generation with nested loops

Question

I made this script which generates all combinations of lowercase letters and numbers and echoes them. It works, but I am wondering if there is a way to simplify the process of adding a new char instead of my current way of having to make a new function for every new character I want to add. Here's my script:

declare -r LIST=$(echo {a..z} {0..9})

function word_generation_2 {
    for char1 in  ${LIST}; do
        for char2 in  ${LIST}; do
            echo ${char1}${char2}
        done
    done
}

function word_generation_3 {
    for char1 in  ${LIST}; do
        for char2 in  ${LIST}; do
            for char3 in  ${LIST}; do
                echo ${char1}${char2}${char3}
            done
        done
    done
}


function word_generation_4 {
    for char1 in  ${LIST}; do
        for char2 in  ${LIST}; do
            for char3 in  ${LIST}; do
                for char4 in  ${LIST}; do
                    echo ${char1}${char2}${char3}${char4}
                done
            done
        done
    done
}


function word_generation_5 {
    for char1 in  ${LIST}; do
        for char2 in  ${LIST}; do
            for char3 in  ${LIST}; do
                for char4 in  ${LIST}; do
                    for char5 in  ${LIST}; do
                         echo ${char1}${char2}${char3}${char4}${char5}
                    done
                done
            done
        done
    done
}


for ((i = 2; i < 6; i++)); do
    word_generation_${i}
done

Output is:

aa

...


99999

I want to keep it like that. First all combinations of 2 chars, then all combinations of 3 chars, etc.

ilkkachu · Accepted Answer · 2016-10-19 11:14:16Z

1

In Bash or something that supports arrays, you could put the character set in an array and loop over the array again, prepending the characters again:

chars=( {a,b,c} )
doubles=()
triplets=()
for c in "${chars[@]}" ; do 
    doubles+=( ${chars[@]/#/$c} )
done
for c in "${chars[@]}" ; do 
    triplets+=( ${doubles[@]/#/$c} )
done
echo "${triplets[@]}"

that prints aaa aab aac ... ccc, and you can repeat as necessary for the longer ones, or turn it into a recursive function. (The ${var//} is a pattern substitution where # marks the start of the string. When it's applied to an array, it applies to all values of the array, one at a time.)

edited Oct 19, 2016 at 11:14

answered Oct 19, 2016 at 9:51

ilkkachu

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Fantastic code right here! thank you. I don't quite get how to print longer chains of characters. How would I print combinations of 3 or 4 characters?

Blai Peidro
– Blai Peidro

2016-10-19 10:10:21 +00:00
Commented Oct 19, 2016 at 10:10
loop over chars again and append to doubles this time, edited

ilkkachu
– ilkkachu

2016-10-19 10:23:51 +00:00
Commented Oct 19, 2016 at 10:23
I've seen that in the first for loop you can actually write:

Blai Peidro
– Blai Peidro

2016-10-19 11:07:22 +00:00
Commented Oct 19, 2016 at 11:07
doubles+=( ${chars[@]/#/$c} ) triplets+=( ${chars[@]/#/$c$c} ) So you don't need new for loops. Last thing is the code prints the output alltogether while I wanted it to be written one combination per line. Any suggestion for this?

Blai Peidro
– Blai Peidro

2016-10-19 11:09:19 +00:00
Commented Oct 19, 2016 at 11:09
doubles+=( ${chars[@]/#/$c} ) how does it working, someone explain me..

user195911
– user195911

2016-10-19 11:12:34 +00:00
Commented Oct 19, 2016 at 11:12

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